This is one-half of a two-site study proposed jointly by Foa and Franklin at the University of Pennsylvania, and Liebowitz and Simpson at Columbia University, who are submitting separate but similar proposals (collaborative CSMD). Obsessive-compulsive disorder (OCD) is prevalent, chronic, and debilitating. Both cognitive behavior therapy (CBT) by exposure and ritual prevention (EX/RP) and serotonin reuptake inhibitors (SRIs) are recommended for OCD. However, recommended doses of the widely used SRIs leave many patients with substantial residual symptoms and a need for more help. This proposal addresses an important problem in treating OCD: how to augment the limited efficacy of SRIs. This study will examine the immediate and long-term value of adding an established CBT for OCD, i.e., EX/RP, to continuing SRI treatment, for reducing residual symptoms and increasing general functioning. Participants will be 136 individuals (68/site) with clinically significant OCD despite having benefited somewhat from an adequate trial of a SRI. While continuing on an SRI, patients will be randomized to adjunctive EX/RP or another CBT, Stress Management Training (SMT). SMT targets generalized anxiety symptoms, but has not been found effective for OCD. As a credible comparison therapy, SMT will control for time, attention, and other non-specific effects of CBT. Both adjunctive CBT treatments will occur twice a week for 2 months. Responders will enter a 6 month Maintenance Phase, during which they will continue their medication and receive monthly 45 min. maintenance sessions. Those who remain in remission will then enter a 6 month Follow-up Phase, in which they will be allowed to reduce or discontinue medication, and will have no further CBT. Non-responders and relapsers will be treated appropriately and evaluated every 3 months. Assessments will focus on OCD symptoms and on general functioning; they will occur during an Acute Phase (0, 1, 2 mos) and every 3 months thereafter (5, 8, 11, 14 months). The proposed sample will allow sufficient power to test both treatment and site effects. This study has several unique features. 1. It offers a model for pharmacotherapy-psychotherapy studies because experts in each modality will deliver both treatments; this guards against expert biases for either treatment. 2. We wanted the results to be directly applicable to OCD patients seen in routine clinical practice. Accordingly, exclusion criteria are few. 3. The EX/RP protocol was designed to maintain efficacy while maximizing practicality. 4. Patients who are unable to remain in the treatment protocol for any reason will continue to be assessed; this will allow us to describe the long-term outcome of the whole sample. Long-term goals are: a) to provide clinicians with new strategies for treating OCD patients who remain symptomatic despite an adequate trial of a SRI and b) to establish effective treatments that reduces the considerable social costs of unremittant OCD.